1. Field of the Invention
This invention relates to a pump for liquid-dispensing containers and the like. More specifically in a preferred embodiment, this invention relates to a finger-operated pump as used on hand-held liquid-spray-dispensing containers.
2. Description of the Prior Art
In the prior art there are a large variety of pump-type dispensers used on hand-held containers of liquid and adapted upon being reciprocated by finger pressure to pump liquid up from the bottom of the container out through a spray nozzle or mechanical break-up button. The bulk of these devices are not concerned with developing pressure within the pump before dispensing commences to develop an effective spray: rather the user is instructed to operate the pump in "quick, short strokes", assuming that if the strokes are quick enough, pressure will be sufficient to develop an adequate spray.
There has been at least one attempt in the prior art to assure that the pressure built up within the pump was adequate prior to the discharge of liquid to the spray head. This is shown in the U.S. Pat. No. 3,865,313 which issued Feb. 11, 1975 to Kondo. In this structure, the pump plunger is encircled by an annular piston which is spring-biased downwardly so that as the plunger descends, displacing liquid, pressure is built up against the spring-biased piston in a kind of "accumulator" effect. Subsequently, a discharge valve is mechanically actuated when the plunger is at the bottom of the stroke causing the liquid to dispense out and create a spray in the head mounted at the top of the plunger.
A disadvantage of a mechanically actuated discharge valve is that the discharge will occur whether or not sufficient pressure has built up because the opening of the discharge valve is contigent only on the plunger reaching the "down" position. This means that it is possible for the pressure build-up to not be sufficient to form a spray as the liquid passes through the break-up button. Discharge may therefore be in the form of a squirt or thin stream of liquid rather than a spray.
In addition, and even when the plunger is depressed in a "quick, short stroke", the pressure at the spray head will drop upon completion of the downstroke to essentially zero because the discharge valve in such a structure remains open until the plunger starts its upward stroke. This can result in poor atomization at the end of the downstroke.